Method for producing target molten steel by taking pig iron as raw material and target molten steel

Abstract

The invention relates to a method for producing target molten steel with pig iron as a raw material and the target molten steel. The mass percent of Cr in the pig iron is 0.60-1.50%, the mass percent of S in the pig iron is 0.12-0.25%, the mass percent of Cr in the target molten steel is smaller than or equal to 0.20%, and the mass percent of S in the target molten steel is smaller than or equal to 0.004%. The method comprises the following steps: carrying out electric furnace smelting on pig iron to reduce the contents of Cr and S in the steel, adding primary molten steel into a converter, carrying out converter smelting to obtain secondary molten steel, carrying out LF refining by using the secondary molten steel, and adding lime and aluminum in the LF refining process to obtain target molten steel. The process route is simple, the preparation efficiency is high, pig iron serves as the raw material, and the good cost advantage is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and rolling, and specifically relates to a method for producing target molten steel using pig iron as raw material and the target molten steel. Background Art

[0002] Pig iron resources have good cost advantages, but because the mass percentage of Cr and S is relatively high, the mass percentage of Cr and S in pig iron is specifically: Cr: 0.60-1.50%, S: 0.12-0.25%. Therefore, when producing steel with low mass percentage of Cr and S, this resource cannot be used efficiently and in large quantities. The main reasons for the inability to use it efficiently include: the smelting process is long, and pretreatment and desulfurization are required before entering the converter; when the Cr content is high, the melting point of the slag will rise rapidly, affecting the normal smelting of the converter to remove P.

[0003] Based on this, a method for producing molten steel with low mass percentage of Cr and S using pig iron is needed to make full use of pig iron resources and reduce costs and increase efficiency. Summary of the invention

[0004] In order to solve all or part of the above problems, the present invention aims to provide a method for producing target molten steel using pig iron as raw material and the target molten steel.

[0005] According to one aspect of the present invention, a method for producing target molten steel using pig iron as raw material is provided, wherein the mass percentages of Cr and S in the pig iron are: Cr: 0.60-1.50%, S: 0.12-0.25%, respectively, and the mass percentages of Cr and S in the target molten steel are: Cr≤0.20%, S≤0.004%; the method comprises:

[0006] The pig iron is smelted in an electric furnace, lime is added into the furnace and oxygen is blown during the smelting process, and steel is tapped without deoxidation after smelting, and top slag is removed to obtain primary molten steel with reduced Cr and S contents;

[0007] The primary molten steel is added into a converter for converter smelting, and during the converter smelting process, a steel raw material with a weighted composition of Cr≤0.10% and S≤0.030% is added into the converter, and the amount of the steel raw material added is equal to 30%-50% of the total amount of the primary molten steel in the converter, so as to obtain secondary molten steel through converter smelting;

[0008] The secondary molten steel is used for LF refining, and lime and aluminum are added during the LF refining process to obtain the target molten steel through LF refining.

[0009] Furthermore, the electric furnace smelting of the pig iron, adding lime and blowing oxygen into the furnace during the smelting process, and tapping the steel without deoxidation after smelting, and removing the top slag to obtain primary molten steel with reduced Cr and S contents further includes:

[0010] The pig iron is smelted in an electric furnace, and electricity is supplied during the smelting process to heat the pig iron to melt and decarburize it, and oxygen is blown into the furnace during the smelting process to reduce the Cr content by using an oxidizing atmosphere; and

[0011] During the smelting process, lime is added to the furnace to reduce the S content. After smelting, the steel is tapped without deoxidation, and the top slag is removed to obtain primary molten steel. The amount of lime added is: 30-70 kg of lime per ton of pig iron.

[0012] Furthermore, the mass percentages of Cr, C and S in the obtained primary molten steel are respectively: C≤0.10%, Cr: 0.20%-0.60%, S: 0.10%-0.20%.

[0013] Furthermore, the mass percentages of Cr, C and S in the obtained secondary molten steel are respectively: C≤0.05%, Cr≤0.13%, S: 0.050%-0.10%.

[0014] Furthermore, the secondary molten steel is used for LF refining, and lime and aluminum are added during the LF refining process to obtain the target molten steel through LF refining. Specifically,

[0015] The secondary molten steel is used for LF refining; lime is added to the top slag during the LF refining process, and 15-25kg of lime is added to each ton of secondary molten steel; aluminum is added during the LF refining process, and 3-6kg of aluminum is added to each ton of secondary molten steel; and the molten steel is heated to above 1580°C to obtain the target molten steel through LF refining.

[0016] Furthermore, flux is added during the LF refining process to improve the fluidity of the top slag.

[0017] Furthermore, the flux is fluorite.

[0018] The present invention also provides a target molten steel, wherein the mass percentages of Cr and S in the target molten steel are: Cr≤0.20%, S≤0.004%; the target molten steel is prepared by the method described in any one of claims 1-7.

[0019] It can be seen from the above technical scheme that the method for producing target molten steel using pig iron as raw material and the target molten steel provided by the present invention have the following beneficial effects:

[0020] The process route of the invention is simple and the preparation efficiency is high; the method of the invention can be effectively used to produce various low-Cr and low-S clean steels; the method of the invention uses pig iron as raw material and has good cost advantages. DETAILED DESCRIPTION

[0021] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0022] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0023] In order to efficiently utilize pig iron resources, an embodiment of the present invention provides a method for producing target molten steel using high-Cr and high-S pig iron as the main raw material: the innovation of this method lies in melting the pig iron and slagging in an electric furnace, then diluting and smelting it in a converter, and finally obtaining the target molten steel through LF refining. The method of the embodiment of the present invention can reduce the mass percentage of Cr and S in the molten steel to: Cr≤0.20%, S≤0.004%. The method of the embodiment of the present invention can be effectively used to produce various low-Cr and low-S clean steels.

[0024] Specifically, the mass percentages of Cr and S in the pig iron are: Cr: 0.60-1.50%, S: 0.12-0.25%, and the mass percentages of Cr and S in the target molten steel are: Cr≤0.20%, S≤0.004%. A method for producing target molten steel using pig iron as a raw material according to an embodiment of the present invention comprises the following steps:

[0025] S001: The pig iron is smelted in an electric furnace, lime and oxygen are added into the furnace during the smelting process, and the steel is tapped without deoxidation after smelting, and the top slag is removed to obtain primary molten steel with reduced Cr and S contents.

[0026] Among them, smelting the pig iron in an electric furnace, adding lime and blowing oxygen into the furnace during the smelting process, tapping the steel without deoxidation after smelting, and removing the top slag to obtain primary molten steel with reduced Cr and S contents further includes:

[0027] The pig iron is smelted in an electric furnace, and electricity is supplied during the smelting process to heat the pig iron to melt and decarburize it, and oxygen is blown into the furnace during the smelting process to reduce the Cr content by using an oxidizing atmosphere; and

[0028] During the smelting process, lime is added to the furnace to reduce the S content. After smelting, the steel is tapped without deoxidation, and the top slag is removed to obtain primary molten steel. The amount of lime added is: 30-70 kg of lime per ton of pig iron.

[0029] The mass percentages of various elements in the primary molten steel obtained by electric furnace smelting of S001 are shown in Table 1:

[0030] Table 1: Mass percentage of each element in primary molten steel

[0031] element C Cr S The remaining elements content ≤0.10 0.20-0.60 0.10-0.20 Unintentional statistics

[0032] As can be seen from Table 1, the mass percentages of Cr, C and S in the primary molten steel are: C≤0.10%, Cr: 0.20%-0.60%, S: 0.10%-0.20%.

[0033] S002: Adding primary molten steel into a converter for converter smelting, and adding steel raw materials with weighted composition of Cr≤0.10%, S≤0.030% into the converter during the converter smelting process, and the amount of steel raw materials added is equal to 30%-50% of the total amount of primary molten steel in the converter, so as to obtain secondary molten steel through converter smelting.

[0034] In this embodiment, the steel raw materials are one or more, and the weighted composition is Cr≤0.10%, S≤0.030%, which means that the total mass percentage of Cr in all added steel raw materials is Cr≤0.10%, and the total mass percentage of S in all added steel raw materials is S≤0.030%.

[0035] The amount of steel raw material added in this embodiment is equal to 30%-50% of the total amount of primary molten steel in the converter. The converter smelting in this embodiment can reduce the content of Cr and S in the molten steel.

[0036] The mass percentages of various elements in the secondary molten steel obtained by electric furnace smelting of S002 are shown in Table 2:

[0037] Table 2: Mass percentage of each element in secondary molten steel

[0038] element C Cr S The remaining elements content ≤0.05 ≤0.13 0.050-0.10 Unintentional statistics

[0039] As can be seen from Table 2, the mass percentages of Cr, C and S in the obtained secondary molten steel are: C≤0.05%, Cr≤0.13%, S: 0.050%-0.10%.

[0040] S003: LF refining is performed using the secondary molten steel, and lime and aluminum are added during the LF refining process to obtain the target molten steel through LF refining.

[0041] In this embodiment, secondary molten steel is used for LF refining, and lime and aluminum are added during the LF refining process to obtain target molten steel through LF refining. Specifically:

[0042] LF refining is performed using secondary molten steel; lime is added to the top slag during LF refining, and 15-25 kg of lime is added per ton of secondary molten steel; aluminum is added during LF refining, and 3-6 kg of aluminum is added per ton of secondary molten steel; and the molten steel is heated to above 1580° C. to obtain target molten steel through LF refining. The mass percentage of each element in the target molten steel finally obtained is shown in Table 3:

[0043] Table 3: Mass percentage of each element in the target molten steel

[0044] element Cr S The remaining elements content ≤0.15 ≤0.004 Adjust as needed

[0045] The mass percentages of Cr and S in the target molten steel are: Cr≤0.15%, S≤0.004%, and the contents of other elements can be adjusted according to the required molten steel.

[0046] The purpose of adding lime is to reduce the sulfur content in molten steel. In the LF refining process, flux can be added as needed to improve the fluidity of the top slag. In order to make the lime react chemically with sulfur as much as possible, stirring can also be performed during the smelting process.

[0047] The method of the embodiment of the present invention reduces the content of Cr and S in molten steel by reducing the content of Cr and S in molten steel in electric furnace smelting, batch dilution, and converter smelting; and after LF refining and deep S removal, the content of Cr and S in steel is effectively reduced to achieve the target molten steel composition. The process route of the embodiment of the present invention is simple and the preparation efficiency is high. The method of the embodiment of the present invention can be effectively used to produce various low-Cr and low-S clean steels.

[0048] In order to facilitate the understanding of the present invention, the specific implementation modes of the present invention are described in detail below in conjunction with examples, but the specific implementation modes of the present invention are not limited to the following examples.

[0049] Embodiment 1:

[0050] The mass percentage of Cr and S in pig iron is: Cr: 1.20%, S: 0.17%, and the other elements are not limited; while the mass percentage of Cr and S in target molten steel is: Cr≤0.20%, S≤0.004%, and the other elements are not limited. The process route of obtaining target molten steel from pig iron is: electric furnace smelting→slag removal→converter smelting→LF refining.

[0051] Among them, the output of steel after removing the top slag of the electric furnace is 148t, and the mass percentage of each component in the steel is as shown in Table 4:

[0052] Table 4: Mass percentage of each element in the primary molten steel obtained after the pig iron in Example 1 was smelted in an electric furnace

[0053] element C Cr S The remaining elements content 0.03 0.40 0.14 Not interested in joining

[0054] The primary molten steel is added into the converter for converter smelting, and then steel raw materials with weighted composition of Cr: 0.02%, S: 0.021% are added, with an addition amount of 70t. After converter smelting, the mass percentage of Cr decreases again, and the mass percentage of S also decreases.

[0055] The mass percentages of the components in the secondary molten steel obtained after converter smelting are as follows in Table 5:

[0056] Table 5: Mass percentage of each element in the secondary molten steel obtained in Example 1

[0057] element C Cr S The remaining elements content 0.02 0.10 0.090 Not interested in joining

[0058] LF refining was performed, and lime and aluminum were added at the same time. The amount of lime added was 20 kg per ton of secondary molten steel, and the amount of aluminum added was 5 kg per ton of secondary molten steel. Fluorite was added as a flux. The amount of fluorite added was 500 kg. The temperature was raised to 1620°C, and strong stirring was performed for 15 minutes for desulfurization to obtain the target molten steel. The mass percentage of each component in the target molten steel is as shown in Table 6:

[0059] Table 6: Mass percentage of each element in the target molten steel obtained in Example 1

[0060] element Cr S The remaining elements content 0.15 0.0025 Adjust as needed

[0061] Embodiment 2:

[0062] The mass percentage of Cr and S in pig iron is: Cr: 0.90%, S: 0.15%, and the other elements are not limited; while the mass percentage of Cr and S in target molten steel is: Cr≤0.10%, S≤0.003%, and the other elements are not limited. The process route of obtaining target molten steel from pig iron is: electric furnace smelting→slag removal→converter smelting→LF refining.

[0063] Among them, the output of steel after removing the top slag of the electric furnace is 150t, and the mass percentage of each component in the steel is as shown in Table 7:

[0064] Table 7: Mass percentage of each element in the primary molten steel obtained after the pig iron was smelted in an electric furnace in Example 2

[0065] element C Cr S The remaining elements content 0.04 0.30 0.13 Not interested in joining

[0066] The primary molten steel is added into the converter for converter smelting, and then steel raw materials with weighted composition of Cr: 0.01%, S: 0.020% are added, with an addition amount of 65t. After converter smelting, the mass percentage of Cr decreases again, and the mass percentage of S also decreases.

[0067] The mass percentages of the components in the secondary molten steel obtained after converter smelting are shown in Table 8:

[0068] Table 8: Mass percentage of each element in the secondary molten steel obtained in Example 2

[0069] element C Cr S The remaining elements content 0.02 0.05 0.070 Not interested in joining

[0070] LF refining was performed, and lime and aluminum were added at the same time. The amount of lime added was 18 kg per ton of secondary molten steel, and the amount of aluminum added was 4.5 kg per ton of secondary molten steel. Fluorite was added as a flux. The amount of fluorite added was 400 kg. The temperature was raised to 1620°C, and strong stirring was performed for 13 minutes for desulfurization to obtain the target molten steel. The mass percentage of each component in the target molten steel is as shown in Table 9:

[0071] Table 9: Mass percentage of each element in the target molten steel obtained in Example 2

[0072] element Cr S The remaining elements content 0.05 0.002 Adjust as needed

[0073] The embodiment of the present invention further provides a method for preparing a target molten steel. The target molten steel refers to molten steel in which the mass percentages of Cr and S are: Cr≤0.20%, S≤0.004%. The target molten steel of this embodiment is prepared by the above method.

[0074] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A method for producing target molten steel using pig iron as raw material, wherein the mass percentages of Cr and S in the pig iron are: Cr: 0.60-1.50%, S: 0.12-0.25%, and the mass percentages of Cr and S in the target molten steel are: Cr≤0.20%, S≤0.004%; characterized in that: The method comprises: The pig iron is smelted in an electric furnace, lime is added into the furnace and oxygen is blown during the smelting process, and steel is tapped without deoxidation after smelting, and top slag is removed to obtain primary molten steel with reduced Cr and S contents; The primary molten steel is added into a converter for converter smelting, and during the converter smelting process, a steel raw material with a weighted composition of Cr≤0.10% and S≤0.030% is added into the converter, and the amount of the steel raw material added is equal to 30%-50% of the total amount of the primary molten steel in the converter, so as to obtain secondary molten steel through converter smelting; The secondary molten steel is used for LF refining, and lime and aluminum are added during the LF refining process to obtain the target molten steel through LF refining.

2. The method according to claim 1, characterized in that The method of smelting the pig iron in an electric furnace, adding lime and blowing oxygen into the furnace during the smelting process, tapping the steel without deoxidation after smelting, and removing the top slag to obtain primary molten steel with reduced Cr and S contents further comprises: The pig iron is smelted in an electric furnace, and electricity is supplied during the smelting process to heat the pig iron to melt and decarburize it, and oxygen is blown into the furnace during the smelting process to reduce the Cr content by using an oxidizing atmosphere; and During the smelting process, lime is added to the furnace to reduce the S content. After smelting, the steel is tapped without deoxidation, and the top slag is removed to obtain primary molten steel. The amount of lime added is: 30-70 kg of lime per ton of pig iron.

3. The method according to claim 2, characterized in that The mass percentages of Cr, C and S in the obtained primary molten steel are respectively: C≤0.10%, Cr: 0.20%-0.60%, S: 0.10%-0.20%.

4. The method according to claim 1, characterized in that The mass percentages of Cr, C and S in the obtained secondary molten steel are respectively: C≤0.05%, Cr≤0.13%, and S: 0.050%-0.10%.

5. The method according to claim 1, characterized in that The method of using the secondary molten steel for LF refining and adding lime and aluminum during the LF refining process to obtain the target molten steel through LF refining is as follows: The secondary molten steel is used for LF refining; lime is added to the top slag during the LF refining process, and 15-25kg of lime is added to each ton of secondary molten steel; aluminum is added during the LF refining process, and 3-6kg of aluminum is added to each ton of secondary molten steel; and the molten steel is heated to above 1580°C to obtain the target molten steel through LF refining.

6. The method according to claim 5, characterized in that Flux is added during LF refining to improve the fluidity of the top slag.

7. The method according to claim 6, characterized in that The flux is fluorite.

8. A target molten steel, wherein the mass percentages of Cr and S in the target molten steel are: Cr≤0.20%, S≤0.004%; characterized in that: The target molten steel is prepared by the method according to any one of claims 1 to 7.